Drop tables are generally known in the art, but suffer from a number of disadvantages. Examples of known drop tables are shown and described in U.S. Pat. No. 2,718,851 to Holdeman and U.S. Pat. No. 2,652,784 to Holmes.
Holdeman discloses an apparatus for removing and replacing the wheels of a passenger car that operates in a pit intersecting a service track over which vehicles may run. As disclosed, for convenience and safety of the workmen, the table is closed between the rails by a floor plate. Holdeman further discloses an air based lifting mechanism
Holmes discloses another drop table where rails are positioned at a fixed distance above a working platform where the working platform and rails move up and down allowing for removal of trucks, axle assemblies and the like. Holmes further discloses a vertical screw based lifting mechanism.
CN202989714, relates to a railway maintenance vehicle having a scissor type mechanism for moving a working platform 22 up and down.
Due to the configuration of these lifting devices, pits must often be larger than about 6 feet deep. Typically, the deeper the pit, the more dangerous the pit is considered. In many cases, government regulating bodies such as OSHA (Occupational Saftey and Health Administration) regulate pits in factories and repair shops based on depth. For example, additional fall prevention safeguards may be required for pits larger than six feet in depth. In addition, some rail yards may be located in areas where soil moisture content progressively increases as the pit depth increases. At increasing depths, there may be too much water content or even ground water present which inhibits proper installation of a machinery pit.
Further, many drop tables may be positioned in a pit with multiple parallel track sections passing through the pit. Therefore, the machinery may need a traversing function that allows it to move between the different track sections for installation and/or removal of various parts such as axles. The use of rails in the bottom of the pit further increases requirements for pit depth as the height of the rails must be added to the clearance requirements for the machinery so that the machinery can drop far enough down into the pit for appropriate repair and replacement operations to be completed.